In the manufacturing of electric and/or electronic components exists an ongoing demand for smaller components while their power density should be increased at the same time. This is particularly true in the manufacturing of inductive elements such as transformers, inductors or chokes. One of the major problems when reducing the size of inductive elements is to dissipate the heat, which is generated within the magnetic circuit, efficiently.
Document EP 0 133 661 shows a transformer type, which is widely known in the art, either in the formation shown or in different variations. Each winding of the transformer is wound on a separate coil body which comprises a flange on each end to hold the windings in the correct position. When the transformer is fitted together, a thin metal foil is inserted between two adjacent coil bodies to provide for electrical isolation as well as for shielding.
Since this transformer does not include an efficient cooling of the circuit, it is not suited for high power applications and its leakage inductance is quite bad.
Another transformer is described in the publication FR 2 476 898. The transformer comprises a magnetic core with three legs where all of the windings of the transformer are formed by a plurality of flat coils. As the coils are positioned directly one after another, they are electrically isolated all of their surface. The coils generally have a rectangular shape, include an air gap and are provided directly around the middle core leg.
This transformer too does not provide for an efficient cooling. The flat coils are electrically isolated which presents an efficient heat dissipation. Furthermore, this type of transformer can not be used in applications, where at least one of the transformer windings shall bed realised with isolated copper wires.
In order to provide transformers that require only a small space, planar transformers where the windings are formed by copper traces that are etched on a printed circuit board, have been introduced. Furthermore, different cooling methods are known to enhance heat dissipation. However, while planar transformers are suited very well in certain applications, they are not useful in other applications.